Intraocular pressure measurements with the Tono-Pen XL® and Perkins® applanation tonometers in horses and cattle

Abstract

The objective of this study was to compare the accuracy between two applanation tonometers, Tono-Pen XL® and Perkins®, in horses and cattle. The eyes of 20 horses and 20 cattle conscious and healthy were evaluated for the in vivo study and both eyes of 5 horses and 5 cattle were used as controls for the postmortem study. In conscious animals, the tonometry was performed with auriculopalpebral nerve block and then topical anesthesia for both tonometers and 1% fluorescein eye drops only for the Perkins tonometer. Readings of intraocular pressure (IOP) in the postmortem study were taken using manometry and tonometry by Tono-Pen XL® and Perkins®. The correlation coefficient (r²) between manometry and applanation tonometers Tono-Pen XL® and Perkins®, in horses, were 0.845 and 0.989, respectively, and in cattle, were 0.772 and 0.988, respectively. The mean IOP values in conscious horses with Tono-Pen XL® and Perkins® were 20.1±3.9mmHg and 20.9±3.2mmHg, respectively, and in conscious cattle, these values were 17.2±2.4mmHg and 17.9±1.4mmHg, respectively. There was a strong correlation between the IOP values obtained by direct ocular manometry and the Tono-Pen XL® and Perkins® tonometers in horses and cattle. There was no statistically significant difference between the mean IOPs obtained with both tonometers in conscious animals; however, there was a difference between the minimum values, which were on average 2-3 mmHg lower with the Tono-Pen XL® tonometer than with the Perkins® tonometer, which justifies a table of normal values differentiated for each tonometer.